1. Field Of The Invention
This invention relates to process signal generators, and, more particularly, to process signal generators for use with radar test devices to produce a substantially delayed replicas of a transmitted radar signal.
2. Description Of Related Art
In various applications, one often faces the need to generate multiple delayed replicas of a radar signal and transmit it back. It is well known that fiberoptic delay lines because of their inherent capability to support very wide bandwidth and large time delays are a good candidate for generating a single delayed version of an input signal. Such an arrangement is shown in U.S. Pat. No. 4,128,759 wherein a plurality of fiberoptic light paths, each having a determinably variant optical propagation delay, are used to generate multiple delayed replicas of a signal. Such a signal generator can be useful to produce delayed replicas of a transmitted radar signal to jam a radar detecting station by overwhelming the station with a plurality of signals.
An example of a prior art fiberoptic delay line is shown in FIG. 1. Therein, prior art fiberoptic delay line 10 receives an input signal 12 which drives a laser diode 14. The optical output of laser diode 14 drives a 1:N fiberoptic splitter 16. The output of fiberoptic splitter 16 is fed into N fiber segments 20 which are of linearly increasing length. The increment of the increasing length corresponds to the minimum delay resolution T.sub.1 . The transmission of each fiber 20 is controlled by an optical switch 18. The outputs of switches 18 drive an N:1 fiberoptic combiner 22 which sums the optical signals and drives a common detector 24. The output of detector 24 passes through buffer 26 before being transmitted as output signal 28.
In prior art fiberoptic delay line 10, when all N optical switches 18 are "on", the output of detector 24 consists of N signal replicas spaced T.sub.1 time apart. In order to create L replicas of a signal with up to R possible replica-to-replica delay values, a total of N=LR fiber segments 20 and switches 18 are needed. Thus, in order to create 64 signal replicas with up to 128 possible replica-to-replica delay values, a total of 8,192 fiber segments 20 and switches 18 are needed. From a hardware point of view, prior art fiberoptic delay line 10 is very inefficient and impractical.